Use of polyester amides for the stabilisation of asphaltenes in crude oil

ABSTRACT

Processes for producing polyester amides, by reacting a polyisobutylene with a first reagent selected from the group consisting of at least monounsaturated acids having from 3 to 21 carbon atoms and derivatives thereof; and a second reagent selected from the group consisting of monoethanolamine and alkylamines of the general formula R—NH 2 , wherein R represents an alkyl group having from 1 to 4 carbon atoms; are described. The polyester amides thus produced and their uses in stabilizing asphaltenes in crude oil and crude oil derivatives are also described.

[0001] This invention relates to certain polyester amides, to a processfor their production, to their use for stabilizing asphaltenes in crudeoil and to a process for preventing the precipitation of asphaltenes incrude oils.

[0002] Crude oil is a complex mixture of various paraffinic and aromatichydrocarbons in which the individual constituents have very differentchemical and physical properties. Accordingly both readily volatile,low-viscosity constituents and wax-like, high-viscosity fractions areobtained in the distillation of crude oil. The second of these twogroups includes petroleum resins and, to a predominant extent,asphaltenes which are colloidally dispersed in the oil phase.

[0003] The asphaltenes consist of a mixture of various saturated,unsaturated and aromatic hydrocarbons, more particularly naphthalenederivatives. Besides these, there are also found heterocyclichydrocarbons which, in part, also contain complexed metal ions. Inaddition, asphaltenes are rich in sulfur, nitrogen and oxygen compounds.Because of their complex composition, asphaltenes are generallycharacterized on the basis of their solubility. Thus, the petroleumfraction insoluble in heptane or pentane, but soluble in toluene isreferred to as asphaltenes, the “dissolution” of asphaltenes involving acomplex process for which there has as yet been no complete theoreticalexplanation (cf. E. Y. Sheu, O. C. Mullins, Asphaltenes—Fundamentals andApplications, Plenum Press, New York, 1995, Chapter I and Chapter III).

[0004] Asphaltenes are present as micelle colloids in the oil phase ofcrude oil, the individual micelles consisting of several differentmolecules. The micelles vary in size according to the temperature andcomposition of the oil phase. For example, it is known that relativelylight aromatic hydrocarbons in crude oil stabilize the asphaltenemicelles. Under the conditions prevailing in petroleum production orrecovery, however, the asphaltenes are often precipitated, which resultsin the formation of highly viscous, wax-like or solid residues on thesurface of the production units and the petroleum-containing formationsurrounding the well. The asphaltene residues block the pores of theformation, which leads to a noticeable reduction in the production ratesand, in the worst case, can make production completely impossible.Asphaltene residues on the surfaces of the production units, for examplethe delivery tube or the casing walls of pipelines or separators, canalso considerably reduce production.

[0005] Accordingly, there are various known methods for keepingasphaltenes dispersed in crude oil and for preventing theirprecipitation. In this regard, DE 197 09 797 describes synergisticmixtures of alkylphenol-formaldehyde resins and certain alkoxylatedamines as asphaltene dispersants. It is known from U.S. Pat. No.4,414,035 that alkylarylsulfonic acid derivatives, for exampledodecylbenzenesulfonic acid, are suitable for dispersing asphaltenes incrude oils.

[0006] However, it has often been found in practice that knownauxiliaries for stabilizing asphaltenes differ very considerably intheir effectiveness according to the nature and origin of the crude oil.This is attributable in particular to the complex and highly variablestructure of the asphaltenes. Accordingly, efforts have been made tofind new asphaltene stabilizers. In addition, asphaltene stabilizersknown in the prior art are often either toxic and/or ecologicallyunsafe. Both for reasons of environmental compatibility of operatingmedia and in the interests of safety at work, attempts are thereforebeing made to avoid using such substances.

[0007] Accordingly, the problem addressed by the present invention wasto provide effective alternatives to the stabilizers known from theprior art for stabilizing asphaltenes in crude oils, even for verydifferent crude oil grades. It has been found that certain polyesteramides solve this problem.

[0008] In a first embodiment, the present application relates topolyester amides obtainable by a two-stage reaction in which (A)polyisobutylene is reacted with at least monounsaturated acidscontaining 3 to 21 carbon atoms or derivatives thereof, preferablycarboxylic anhydrides thereof, for at least 3 h, ither (A.1) in the presnce of radical initiators at temperatures of 65 to 100° C. or (A.2)without radical initiators, but optionally in the presence of Lewisacids, at 150 to 250° C., and in the second step (B) an alkylamine withthe general formula R—NH₂, in which R is an alkyl group containing 1 to4 carbon atoms, is added to the product thus obtained and the mixture isstirred at 60 to 100° C. and then cooled and the end product is isolatedin known manner.

[0009] The polyester amides according to the invention are based onpolyisobutylene, a raw material known to the expert which isindustrially obtained by polymerization of isobutylene. Particulars ofthe production and properties of this class of compounds can be found inUllmanns Encyclopedia of Industrial Chemistry, Sixth Edition, 2000Electronic Release—Butenes—Chemical Properties. The polyisobutyleneshave molecular weights of 500 to 50,000, preferably in the range from1,000 to 25,000 and more preferably in the range from 1,500 to 15,000.Beside pure isobutylene, it may also be preferred to use copolymerswhich contain at least 50% of isobutylene monomers, and furthermonomers.

[0010] The polyisobutylenes are introduced into a reaction vessel attemperatures of at least 60° C., preferably at temperatures of 65 to 95°C. and more particularly at temperatures of 75 to 85° C. and theunsaturated acids are then added.

[0011] These acids or their derivatives are at least mono-olefinicallyunsaturated and preferably contain 3 to 7 carbon atoms. The anhydridesare particularly preferred. A preferred anhydride is maleic anhydride.However, maleic acid or fumaric acid or their esters or acrylic acid,methacrylic acid and derivatives thereof are also suitable components instep (A).

[0012] In one variant, the reaction in the first step takes place in thepresence of radical initiators, preferably azo-bis-isobutyronitrile(AIBN) and/or other radical initiators known to the expert, for exampledibenzoyl peroxides, radical initiators with half lives at 60 to 70° C.of 10 hours being particularly preferred. The following radicalinitiators are mentioned by name here: dibenzoyl peroxide, tert-amylperoxy-2-ethylhexanoate, tert-butyl peroxi-2-ethylhexanoate, tert-butylperoxyisobutyrate and tert-butyl monoperoxymaleate.

[0013] Alternatively, it is also possible to work without radicalinitiators. The reaction according to (A.2) systematically represents anene reaction, it being possible to carry this out in the presence ofcatalysts selected from the group of Lewis acids. Suitable Lewis acidsare, for example, the bromides of phosphorus and aluminum, the chloridesof boron, aluminum, phosphorus, bismuth, arsenic, iron, zinc and tin.However, it is preferred to work without Lewis acids and to react thereactants polyisobutylene and carboxylic acid directly with one another.The reaction temperature in the case of variant (A.2) is higher than for(A.1), namely in the range from 150 to 250° C.

[0014] Preferably, step (A) of the process according to the inventiontakes place under an inert atmosphere, i.e. for example argon or,preferably, nitrogen. The ratio by weight of polyisobutylene tocarboxylic anhydride is preferably in the range from 200:1 to 1:200.Ratios by weight of 100:1 to 1:100 are preferred. Ratios by weight of5:1 to 20:1 are particularly preferred, ratios by weight of 10:1 to 15:1being most particularly preferred. The choice of suitable ratios byweight is governed by the molecular weight of the components used andmay readily be made by the expert.

[0015] The reaction time is at least 3 h at at least 60° C. in the case(A.1) or at least 150° C. in the case (A.2), higher temperatures andlonger reaction times, for example 4 to 8 h or 5 to 7 h, beingpreferred. Thereafter, a suitable amine with the formula R—NH₂ may beadded to the reaction mixture. However, the reaction mixture may alsofirst be freed from unreacted anhydride, preferably by distillationunder reduced pressure, and the reaction mixture thus worked upsubsequently reacted with the amine at a temperature of at least 50° C.Under the effect of the exothermic reaction of thepolyisobutylene/anhydride product with the amine, the temperature in thereaction vessel rises to around 100° C. The mixture containing the endproduct then cools down again and may then be used without furtherpurification. Process steps (A) and (B) may be carried out in a singlereaction stage or in two separate stages either continuously or inbatches.

[0016] The amines of the formula R—NH₂ are known compounds,monoethanolamine preferably being selected. The ratio by weight betweenpolyisobutylene and amine is preferably between 100:1 and 10:1. Therange from 75:1 to 10:1 is particularly preferred, the range from 50:1to 15:1 being most particularly preferred.

[0017] The present application also relates to a process for theproduction of polyester amides in which, in step (A), polyisobutylene isreacted with carboxylic anhydrides for at least 3 hours, either in thepresence of radical initiators at temperatures of 65 to 100° C. orwithout radical initiators, but optionally in the presence of Lewisacids, at 150 to 250° C., and, in step (B), an alkylamine with thegeneral formula R—NH₂, in which R is a C₁₋₄ alkyl group, is added to theproduct thus obtained and the mixture is stirred at 60 to 100° C. andthen cooled and the product is isolated in known manner.

[0018] The polyester amides described in the foregoing are surprisinglyeffective as asphaltene dispersants. In the context of the presentapplication, asphaltenes are those constituents of crude oil which,according to DIN 51595 (Dec. 1983), precipitate when crude oil isdissolved with 30 times its volume of heptane at 18 to 28° C. and whichare soluble in benzene. Asphaltenes can form as solids on the surfacesof production units in petroleum production, production units beingunderstood to be any installations which come into direct contact withthe oil. These include, for example, the delivery tube, the well casingand any other oil-carrying pipes, pipelines, tankers or separators,pumps and valves. The surfaces of these production units generallyconsist of metal, more especially steel. However, production units alsoinclude the processing steps of the crude oil after its actualproduction, for example working up of the crude oil fractions bydistillation. Asphaltene residues can aldo occur in the transport ofcrude oil through pipelines and during its storage and can thus impedeproduction. Solid asphaltene residues are also formed on the surface ofthe petroleum-containing formation surrounding the well where they blockthe pores of the rock, resulting in a noticeable reduction in output.

[0019] Crude oil is understood to be the unrefined petroleum comingdirectly from the ground. This unrefined petroleum consists of complexmixtures of, predominantly, hydrocarbons with densities of 0.65 to 1.02g/cm³ and calorific values of 38 to 46 MJ/kg. The boiling points of themost important constituents of crude oil are in the temperature rangefrom 50 to 350° C. (cf. Römpp, Chemielexikon, Vol. 2, 1997, pages 1210to 1213).

[0020] The use of the polyester amides in accordance with the invention,i.e. their addition to crude oils, effectively prevents theprecipitation of asphaltenes and the formation of residues. In order toprevent the precipitation of asphaltenes, it is of advantage to add thepolyester amides to the crude oil in quantities of 50 to 2500 ppm,preferably in quantities of 100 to 1000 ppm and more particularly inquantities of 150 to 500 ppm (active substance). In addition, polyesteramides with flash points of at most 80° C. are preferably used. Thepolyester amides according to the invention can also be usedsuccessfully for asphaltene inhibition in crude oil derivatives,so-called fuel, middle distillates or residual fuels.

[0021] The present invention also relates to a process for preventingthe precipitation of asphaltenes from crude oils and crude oilderivatives, in which polyester amides corresponding to the foregoingdescription are added to the crude oils as stabilizers in quantities of100 to 2500 ppm.

[0022] The present technical teaching also encompasses the use of thepolyester amides in the form of dilute solutions in aromatic solvents,preferably toluene. These dilute solutions contain the polyester amidesin quantities of preferably 2 to 50% by weight, more preferably 2 to 20%by weight and most preferably 2 to 15% by weight. Such formulations mayalso contain other additives, such as corrosion inhibitors or defoamers.

EXAMPLES

[0023] Production of the Polyester Amides:

Example 1

[0024] 550 g of polyisobutylene (Glissopal 1000, BASF) were introducedinto a reactor at 80° C. and 54 g of maleic anhydride were subsequentlyadded. 6 g of AIBN were added to the two-phase mixture with vigorousstirring. After a reaction time of 5 h at 80° C., 34 g ofmonoethanolamine were added to the reaction mixture. After the onset ofthe exothermic reaction, the temperature rose to 100° C. After thetemperature had fallen to 80° C., the product according to the inventioncould be isolated.

Example 2

[0025] 550 g of polyisobutylene (Glissopal 1300, BASF) were introducedinto a reactor at 80° C. and 42 g of maleic anhydride were subsequentlyadded. 6 g of AIBN were added to the two-phase mixture with vigorousstirring. After a reaction time of 5 h at 80° C., 26 g ofmonoethanolamine were added to the reaction mixture. After the onset ofthe exothermic reaction, the temperature rose to 100° C. After thetemperature had fallen to 80° C., the product according to the inventioncould be isolated.

Example 3

[0026] 550 g of polyisobutylene (Glissopal 1000, BASF) were introducedinto a reactor at 70° C. and 54 g of maleic anhydride were subsequentlyadded. 6 g of AIBN were added to the two-phase mixture with vigorousstirring. After a reaction time of 5 h at 80° C., the unreacted maleicanhydride (30 g) was removed by distillation.

Example 4

[0027] 0.54 g of monoethanolamine was added at 60° C. to 100 g of theproduct obtained in Example 3. After a reaction time of 1 h at 60° C.,the reaction product was decanted.

Example 5

[0028] 550 g of polyisobutylene (Glissopal 1300, BASF) were introducedinto a reactor at 70° C. and 42 g of maleic anhydride were subsequentlyadded. 6 g of AIBN were added to the two-phase mixture with vigorousstirring at 65° C. After a reaction time of 5 h at 80° C., the unreactedmaleic anhydride (17 g) was removed by distillation.

Example 6

[0029] 0.54 g of monoethanolamine was added at 60° C. to 100 g of theproduct obtained in Example 5. After a reaction time of 1 h at 60° C.,the reaction product was decanted.

Example 7

[0030] 550 g of polyisobutylene (Napvis 10) were introduced into areactor under a stream of nitrogen at 200° C. Then, over the course of 3hours, a total of 56 g of maleic anhydride are added in severalportions. The temperature is increased to 210° C., and the mixture isafter-reacted at this temperature for 5 hours. The mixture is cooled to150° C. and passed over a glass suction filter in order to obtain theproduct of the invention according to (A.2).

Example 8

[0031] 550 g of polyisobutylene (Napvis 5) were introduced into areactor under a stream of nitrogen at 200° C. Then, over the course of 3hours, a total of 69 g of maleic anhydride are added in severalportions. The temperature is increased to 210° C., and the mixture isafter-reacted at this temperature for 5 hours. The mixture is cooled to150° C. and passed over a glass suction filter in order to obtain theproduct of the invention according to (A.2).

Example 9

[0032] 550 g of polyisobutylene (Napvis 30) were introduced into areactor under a stream of nitrogen at 200° C. Then, over the course of 3hours, a total of 41 g of maleic anhydride are added in severalportions. The temperature is increased to 210° C., and the mixture isafter-reacted at this temperature for 5 hours. The mixture is cooled to150° C. and passed over a glass suction filter in order to obtain theproduct of the invention according to (A.2).

[0033] Testing of the Dispersing Properties:

[0034] The test is based on the fact that asphaltenes are soluble inaromatic hydrocarbons but not in aliphatic hydrocarbons. Accordingly,dispersants can be tested by dissolving the oil or extracted asphaltenesin an aromatic solvent and then adding a nonaromatic solvent to producea deposit.

[0035] Since asphaltenes are dark in color, the size of the deposit canbe determined by UV-spectroscopic measurement of the supernatant liquid.

[0036] Dispersing Test—Procedure

[0037] a) A 25% oil solution in toluene is filtered to eliminateimpurities.

[0038] b) Introduce 9.5 ml of heptane as precipitant for asphaltenes and0.5 ml of toluene/dispersant mixture (25:1) into a small graduated glasstube holding a good 10 ml and shake thoroughly. This corresponds to adispersant concentration of 2000 ppm. The quantity of dispersant may bevaried as required. Pure toluene is used for blank tests.

[0039] c) Introduce 0.1 ml of the filtered oil solution into the glasstube and again shake thoroughly.

[0040] d) Leave the whole standing for 2 hours away from any vibration.The precipitated asphaltenes should be able to collect at the bottom ofthe glass tube.

[0041] e) After this time, the volume of sediment is estimated from thegraduation, the appearance of the sample as a whole is recorded and 1 mlof the supernatant phase is then carefully taken up in a pipette.

[0042] f) The quantity taken up is dissolved in 5 ml of a 99:1 mixtureof toluene and triethanolamine and the maximum absorption is measured at700 nm in a UV spectrometer.

[0043] Results

[0044] Crude oils of differing grades were tested as described above.The results obtained with a standard prior art dispersant (DSA 900,Anticor) are compared with those achieved with compounds 1 to 6according to the invention in Tables 1 to 3 below. In order to make theresults comparable, the absorption values of the samples were divided bythe absorption value of the blank sample (pure solvent), the resultbeing shown in the Tables as relative absorption. The nearer the valuesare to 1.0, the better the effect of the dispersant was. TABLE 1Venezuela 1 Venezuela 2 Venezuela 3 Dispersant Rel. absorption Rel.absorption Rel. absorption DSA 900 0.72 0.78 0.77 1 0.77 0.81 0.81 20.82 0.86 0.83 3 — — — 4 — — — 5 0.81 0.85 0.81 6 0.83 — —

[0045] TABLE 2 Mexico Austria Norway Dispersant Rel. absorption Rel.absorption Rel. absorption DSA 900 0.63 0.47 0.76 1 0.76 0.47 0.66 20.76 0.54 0.76 3 — 0.55 0.76 4 — 0.54 0.79 5 0.75 0.51 0.64 6 — 0.470.64−

[0046] TABLE 3 Algeria Dispersant Rel. absorption DSA 900 0.63 1 0.63 2— 3 — 4 — 5 0.68 6 0.71

[0047] It can be seen that the dispersants according to the inventionall achieve better results than the prior art product.

1. Polyester amides obtainable by a two-stage reaction in which (A) apolyisobutylene is reacted with at least monounsaturated acidscontaining 3 to 21 carbon atoms or derivatives thereof, either (A.1) inthe presence of radical initiators at temperatures of 65 to 100° C. or(A.2) without radical initiators, optionally catalyzed by Lewis acids,at 150 to 250° C., and (B) an alkylamine with the general formula R—NH₂,in which R is an alkyl group containing 1 to 4 carbon atoms, is added tothe product thus obtained and the mixture is stirred at 60 to 100° C.and then cooled and the product is isolated in known manner. 2.Polyester amines as claimed in claim 1, characterized in that, in step(A), the polyisobutylenes are reacted with carboxylic anhydrides. 3.Polyester amides as claimed in claim 1 or 2, characterized in thatpolyisobutylene and carboxylic anhydride are used in a ratio by weightof 5:1 to 20:1 and preferably 10:1 to 15:1.
 4. Polyester amides asclaimed in claims 1 to 3, characterized in that the ratio by weight ofpolyisobutylene to alkylamine is 100:1 to 10:1.
 5. Polyester amides asclaimed in claims 1 to 4, characterized in that maleic anhydride isused.
 6. Polyester amides as claimed in claims 1 to 5, characterized inthat monoethanolamine is used as the alkylamine.
 7. Polyester amides asclaimed in claims 1 to 6, characterized in that azo-bis-isobutyronitrile(AIBN) and/or dibenzoyl peroxide and derivatives thereof is/are used asthe radical initiator(s).
 8. Polyester amides as claimed in claims 1 to6, characterized in that boron trifluoride, the bromides of phosphorusand aluminum, the chlorides of boron, aluminum, phosphorus, bismuth,arsenic, iron, zinc and tin are selected as Lewis acids.
 9. Polyesteramides as claimed in claims 1 to 8, characterized in that thepolyisobutylene can also comprise other monomers in addition to at least50% isobutylene as monomer.
 10. A process for the production ofpolyester amides, characterized in that (A) a polyisobutylene is reactedwith at least monounsaturated acids containing 3 to 21 carbon atoms orderivatives thereof, either (A.1) in the presence of radical initiatorsat temperatures of 65 to 100° C. or (A.2) without radical initiators,optionally catalyzed by Lewis acids, at 150 to 250° C., and (B) analkylamine with the general formula R—NH₂, in which R is a C₁₋₄ alkylgroup, is added to the product thus obtained and the mixture is stirredat 60 to 100° C. and then cooled and the product is isolated in knownmanner.
 11. A process as claimed in claim 10, characterized in thatsteps (A) and (B) are carried out in separate stages.
 12. The use ofpolyester amides claimed in claim 1 as stabilizers for asphaltenes incrude oils and crude oil derivatives.
 13. The use claimed in claim 12,characterized in that polyester amides with a flash point of at most 80°C. are used.
 14. The use claimed in claims 12 to 13, characterized inthat the polyester amides are added to the crude oils in quantities of50 to 2500 ppm, preferably in quantities of 100 to 1000 ppm and moreparticularly in quantities of 150 to 500 ppm.
 15. A process forpreventing the precipitation of asphaltenes from crude oils,characterized in that polyester amides claimed in claim 1 are added tothe crude oils or their derivatives as stabilizers in quantities of 100to 2500 ppm.